The invention relates to an apparatus for communicating information about a taking lens, and more particularly, to such apparatus which communicates functional information about an interchangeable lens barrel which houses the taking lens such as the maximum F-number of the lens, the focal length of the lens or the like to a camera body in a magnetic manner.
In a single lens reflex camera using an interchangeable lens, it is necessary to provide the camera body with functional information about a taking lens mounted on the camera. Such information can include the maximum F-number, minimum diaphragm value, the number of steps of available for the diaphragm values of the lens, the correction of an indication of the opening of the lens or the like. Conventional communication means may comprise a mechanical member such as a diaphragm interlocked member, a member interlocked with the maximum F-number or the like, the displacement of which is utilized to derive functional information. Alternatively, a plurality of electrical contacts may be disposed on the lens and the camera body, respectively, so that information may be communicated therebetween through the conduction or non-conduction between the contacts. However, it will be seen that these techniques represent information communication of so-called contact type wherein an error in the displacement of a mechanical lever may result in the inaccuracy of information or a poor contact between the electrical contacts results in a reduced reliability. In addition, resistors or contacts of a noble metal which provide good conductors must be provided on the part of the camera in order to convert the oncoming signals into electrical signals which are suitable for use in a logic circuit, thus causing the mechanism to be complicated.
Recently, an arrangement for information communication has been proposed wherein an interchangeable lens barrel is provided with PROM (programmable read-only memory) in which information such as the maximum F-number or the like is stored so that the information may be read by an assembly provided on the part of the camera body (see Japanese Laid-Open Patent Application No. 108,628/1979). However, a multiple-pin connector is used to provide a connection between the lens and the camera body, presenting the same difficulty as mentioned above.